Stockholders' Equity - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended			3 Months Ended						9 Months Ended			1 Months Ended			9 Months Ended	12 Months Ended
	Jul. 31, 2013	Apr. 30, 2013	Feb. 28, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Apr. 30, 2013 Minimum [Member]	Apr. 30, 2013 Maximum [Member]	Oct. 31, 2013 Subsequent Event [Member]	Sep. 30, 2013 Restricted Stock Units (RSUs) [Member]	Dec. 31, 2011 Restricted Stock Units (RSUs) [Member]	Dec. 31, 2010 Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSU's issued				385,000						385,000		301,000					71,000	63,000
Performance of RSU's Vesting																	100% or 40% on April 1, 2014	100% or 40% on April 1, 2013
Compensation expense Estimate vesting																	100.00%	100.00%
Modified Estimate vesting of RSU's																0.00%		0.00%
Dividend declared and paid per share				$ 0.15	$ 0.15	$ 0.15	$ 0.14	$ 0.14	$ 0.14
Aggregate dividend declared for the year										$ 9.4	$ 9.5
Dividend declared				$ 0.15			$ 0.14			$ 0.45	$ 0.42				$ 0.15
Aggregate cost of repurchase of common stock										320.0
Authorized to Purchase of common stock under the stock repurchase program	25.0		50.0							385.0
Cumulative repurchase of common stock				12,200,000						12,200,000
Repurchase of common Stock										3,000,000
Cumulative aggregate cost of repurchase of common stock										109.2
Repurchase of self-tender		130
Common stock price per share													$ 32.00	$ 36.00
Increment in per share value		$ 0.25
Purchase of common stock		2,054,732
Purchase price of common stock		$ 36.00
Aggregate price of stock		74.0
Expenses related to tender offer		1.1
Treasury stock, retired										11,700,000
Carrying value of retired stock										$ 303.0